The invention relates generally to processing a surface on a substrate, e.g., depositing a coating on or etching by using a carbon containing ion bean using a gridded ion source, particularly an RF or microwave plasma source.
Ion beam processing has many applications in microelectonics device fabrication. It is used, for example, in the production of high frequency microwave integrated circuits and thin magnetic heads.
In surface modification or ion beam etching, generally known as xe2x80x9cion millingxe2x80x9d, a beam of ions is extracted from a plasma ion source by electrostatic methods and is used to remove material from a substrate mounted in the path of the beam. In reactive ion milling methods, certain chemical(s) are introduced to the ion source or to the etching chamber which cause chemical reactions to occur on the substrate as part of the milling process. Often the chemical process is affected by energetic assistance by the plasma (in the ion source) and/or the ion beam.
There are two basic configurations for ion beam deposition. In xe2x80x9cprimaryxe2x80x9d or xe2x80x9cdirectxe2x80x9d ion beam deposition, an ion beam source is used to produce a flux of particles, including constituents of the desired film, which are accumulated at the substrate. In one type of xe2x80x9cprimaryxe2x80x9d ion beam deposition, the deposited material is formed by reactive means from precursor chemicals introduced to the ion source, usually in the gas phase. An example of great practical value is the production of diamond-like carbon films by direct ion beam deposition from an ion source operated on hydrocarbon gas(es), such as methane.
Another configuration in which ion beams can be used for thin film deposition is commonly known as xe2x80x9csecondary ion beam depositionxe2x80x9d, or xe2x80x9cion beam sputteringxe2x80x9d. In this method, an ion beam comprising particles which are not essential to the deposited film are directed at a target of the desired material so as to sputter it, with the sputtered target material being collected on the substrate. Secondary ion beam deposition can be a completely inert sputtering process. Alternatively, certain chemicals can be added to the ion source or elsewhere in the deposition chamber to alter the chemical properties of the deposited film either by reaction with the target material or with the substrate. This can be done with or without energetic activation by the ion source plasma or the ion beam.
DC sources have disadvantages compared with other sources for etching and thin film deposition techniques in terms of ion source maintenance and reactive gas compatibility. Ion beam sources with filament type cathodes, for example, are the easiest to operate and maintain but require frequent replacement of the filament assembly. Furthermore the hot filaments are rapidly attacked in the plasma state by gases which are useful for thin film deposition and etching, such as hydrocarbon, oxygen, hydrogen, and fluorinated gases. Ion sources equipped with hollow cathodes are difficult to maintain. Also, they generally cannot be operated with high concentrations of reactive gas because the hollow cathodes are easily contaminated and must be protected by continuous purging with inert gas. Cold cathodes can be more easily maintained and are compatible with some reactive gases but have other limitations, such as generally low ion beam density, and poor beam collimation. These shortcomings of DC sources can hinder the implementation of ion beam processes in manufacturing processes.
In contrast with DC sources, many RF sources do not require any discharge electrodes directly in contact with the plasma. However, an electrode must be provided to control the plasma potential and provide for charge compensation of the plasma. For example, in U.S. Pat. No. 5,198,718 it is performed by the xe2x80x9cscreenxe2x80x9d grid portion of the ion optics.
In general, plasma and radical concentrations are quite sensitive to source surface conditions and temperature. Stability improvement can be achieved by special source conditioning procedures. However, the problems of aging and irreproducibility become more complicated if conditioning of the source internal surfaces and source operation is accompanied with deposition on the walls and electrodes of high electrical resistivity precipitates. Changes in the conductivity of the electrode surfaces can cause charge build-up in the ion source by inhibiting electrical current flow between the plasma and the electrode which is used to control the plasma potential. Charge build-up inevitably results in arcing (electrical breakdowns) and flaking-off of the precipitates. This phenomenon leads to process irreproducibility, significant reduction of operation time, issues of electrostatic discharge (ESD) damage to the substrate under process, and increase of macroparticulate contamination. These limitations greatly hinder the implementation of methods using hydrocarbon or halocarbon precursor gases in practical applications.
It is an object of the present invention to provide a highly repeatable, long duration repetitive processing (etch or deposition) of a surface on a substrate using a gridded ion source, especially an RF or microwave plasma source, for operation with reactive gases containing carbon, such as hydrocarbons or halocarbons, that form high electrical resistivity precipitates inside of the source.
Another object of the present invention to achieve low macroparticulate ion beam processing.
Another object of the present invention to minimize ESD effects during ion beam processing.
The foregoing objects can be achieved according to the present invention by using a multistep procedure that includes the actual ion beam processing step combined with the thermal and chemical conditioning of the ion source, and special cleaning steps. This procedure is very effective in accomplishing repeatable processing conditions for the actual ion beam processing step for a significant number of runs, e.g., generally greater than about 50 runs and more particularly greater than about 1000 runs.
Moreover, this invention minimizes accumulation of precipitates in the source and reduces macroparticle agglomeration and delamination (flaking), providing a low level of macroparticle generation in the system during ion beam processing. The method is especially beneficial for sustaining stable ion beam operation in the actual ion beam processing steps and in minimizing electrostatic discharge.
In accordance with the invention, the subject method comprises, prior to deposition or etch, the steps of providing an inert gas plasma in the source to establish steady-state thermal conditions in the source, carbon containing plasma conditioning of the source, and ion beam stabilization. A cleaning procedure is performed by removal of the precipitates from the source and the ion beam optics, or areas of the source and the ion beam optics which are responsible for provision of an electrical conduction path during ion beam extraction. The removal of precipitates is achieved by an inert ion assisted reactive oxygen etching process, or by inert ion beam sputtering.
Other features and advantages of the present invention will be further described and more readily apparent from a review of the detailed description and preferred embodiments, which follow.